Child-birth assisting system

ABSTRACT

The childbirth-assisting device uses an automatically synchronized expandable pneumatic girdle to externally augment the secondary force of labor. The girdle through which the pressure is applied is fitted around the abdomen of the woman. An inflatable bladder within the girdle is inflated to create a downward pressure on the abdomen upon detection of a contraction. External pressure monitors which detect contractions may be attached directly to the girdle, and the girdle is configured to assure that the bladder is correctly positioned at all times. A member may be provided to prevent multiple uses of a girdle to assure the integrity of the girdle during use.

This is a continuation-in-part of application Ser. No. 08/086,099, filedJun. 30, 1993, now U.S. Pat. No. 5,405,356.

FIELD OF THE INVENTION

The invention generally relates to the field of labor assisting devices,and specifically to a device which simulates the secondary force oflabor.

BACKGROUND OF THE INVENTION

A normal labor process is divided into three stages. Among these stages,the first and second stages are the crucial ones which are directlyinvolved in the delivery of fetus. The first stage of labor begins withthe onset of rhythmic uterine contraction and ends at the completedilation of the cervix which is about 10 cm in diameter. The completedilation of the cervix marks the beginning of the second stage of laborwhich ends immediately after the birth of the fetus. The third stage oflabor extends from the birth of the baby to the complete expulsion ofthe placenta. The labor progress is driven by two types of labor forces.The primary force is produced by the involuntary contractions of uterinemuscle. The secondary force is produced by the increase ofintra-abdominal pressure through voluntary contractions of the abdominalmuscles and diaphragm. These forces cause an increase of intrauterinepressure to provide a critical expulsion force on fetus.

As often seen in clinical practice, systemic analgesic drugs, epiduralanesthesia and long duration of exhaustive labor all can lead to theweakening of secondary force, and sequentially to delayed labor durationor even dystocia (arrest of labor). Numerous clinical studies havecorrelated a prolonged labor duration and dystocia with many undesirableoutcomes, such as higher rate of infant mortality, neonatal seizures andpostpartum hemorrhage. To solve these serious problems, clinicalinstruments (forceps or vacuum suction) or cesarean section are oftenrequired to terminate labors. However, both instrumental delivery andcesarean section are far from trouble-free. While a cesarean section isbasically safe, it remains a major surgical procedure. Patients who givebirth by cesarean section are at much greater risk of childbirth-relatedillness or death than women who deliver vaginally. Also, the averagecesarean birth has a length of hospital stay double that of a normaldelivery and costs up to three times as much. Instrumental delivery alsohas limitations and may result in numerous complications including headand facial injuries to fetus. Therefore, it is in the best interest ofboth mother and fetus to prevent the incidence of prolonged duration oflabor or dystocia.

One method of decreasing the incidence of prolonged labor is oxytocininfusion, which is commonly used in clinical practice to increase theprimary labor force by directly inducing uterine contraction. Clinicalevidence has demonstrated that oxytocin alone can only partially solvethe problem of prolonged labor and dystocia associated with epiduralanesthesia. However, a high incidence of cesarean section still occursin patients receiving epidural anesthesia in spite of a high dosage ofoxytocin infusion. Furthermore, high doses of oxytocin has beenimplicated in uterine tetanus and in some adverse neonatal outcomes,including fetal asphyxia.

Devices directed toward assisting in delivery are disclosed in the priorart. In the apparatus of Heidenwolf (U.S. Pat. No. 2,597,637, issued May20, 1952), an inflatable bladder is held against the woman's upperabdomen by a wide belt. Extending from the bottom of the belt is a pairof straps which, in turn, attaches to straps surrounding the upperthighs. This structure holds the belt down to prevent slippage.

In the birth-assisting pneumatic cuff of Lee (U.S. Pat. No. 5,174,281,issued Dec. 29, 1992), an inflatable bladder fits over and around thewoman's abdomen and is manually inflated and deflated in coordinationwith the patient's voluntary straining during the second stage of labor.This device applies pressure equally to the entire abdomen.

The Chinese patent of Fei Chao (Chinese Patent No. 2198, issued in 1989)teaches an abdominal girdle which has a generally triangular bladder (tomatch the rough contour of the uterus) which is placed over thepatient's abdomen. The bladder is inflated manually in coordination withthe woman's contractions to apply a downward pressure on the abdomen,assisting in forcing the fetus downward. While the girdle itself is veryeffective, the manual control of the inflation/deflation may not beeasily accepted by physicians who may be reluctant to rely on a devicewhich could be easily subject to human error with serious consequences.

Related prior art may be seen in the areas of anti-G pressure suits andin inflatable tourniquets and splits. Examples of pressure suits aretaught by Crosbie et al. in U.S. Pat. No. 4,534,338, issued Aug. 13,1985, and Van Patten, U.S. Pat. No. 4,736,731, issued Apr. 12, 1988.These suits inflate in response to changes in the rate of accelerationof an aircraft. Poole, et al. (U.S. Pat. No. 4,531,516, issued Jul. 30,1985), Manes (U.S. Pat. No. 4,548,198, issued Oct. 22, 1985) and Kitchinet al. (U.S. Pat. No. 4,520,820, issued Jun. 4, 1985) teach inflatabledevices for first aid applications. The latter two patents includedisclosure of controllers for maintaining constant pressure, howevernone of these patents addresses synchronization of inflation/deflationas would be required for a labor- and delivery-assisting device.

BRIEF SUMMARY OF THE INVENTION

It is an advantage of the present invention to provide a device forassisting in delivery by simulating the secondary force of labor.

It is another advantage of the present invention to provide achildbirth-assisting device which is synchronized with uterinecontractions.

Still another advantage of the present invention is to provide a meansfor preventing prolonged labor while avoiding cesarean section.

In an exemplary embodiment, the childbirth-assisting device uses anautomatically synchronized expandable pneumatic girdle to externallyaugment the secondary force of labor. The pneumatic girdle with agenerally triangular bladder (as taught by Fei Chao) is fitted aroundthe abdomen of the woman and the girdle is inflated to create a downwardpressure on the abdomen when a contraction occurs. The synchronizationof the girdle's inflation and the contractions is provided by amicroprocessor-based electronic controller which receives a signal froman intra-uterine monitor indicating a contraction and commands thegirdle to inflate at a certain rate until a preset intra-uterinepressure is attained. Once the intra-uterinepressure reaches the pre-setpressure, the girdle pressure is maintained until the offset of thecontraction is detected, at which time the girdle is deflated. Theelectronic controller, with programming utilizing rule-based methods,constantly monitors and initiates alarms for hazardous conditionsincluding excessively long contraction periods, paired contractions,skewed contractions and other types of irregular contractions. Thecontroller controls the girdle pressure according the stage of labor anddistinguishes between actual and "false" contractions, which may bedetected by the intrauterine monitor when the patient moves.

The childbirth assisting device can potentially be used in both thefirst stage and the second stage of labor. During the first stage oflabor, the device can increase the abdominal pressure, aiding in theeffacement of the cervix and hastening the descent of fetus and thecervical dilation process. During the second stage of labor, the devicecan provide a critical expulsion force for delivery of the fetus.

The childbirth assisting device can efficiently and safely preventprolonged duration of labor and dystocia due to systemic analgesia,epidural anesthesia, or maternal exhaustion, which can lead to reductionof the cesarean section rate and rate of instrumental delivery. Sinceweakening of the secondary labor force is particularly common inpatients receiving epidural anesthesia, the device can effectivelyprevent weakening of the secondary labor force under anesthesia,enabling a safer and less painful delivery.

By reinforcing the secondary labor force, the childbirth assistingdevice can further reduce the rate of cesarean section associated withdystocia and also lower the dosage of oxytocin. Functioning throughdifferent mechanisms, the device can be used to complement the benefitsof oxytocin in clinical practice.

BRIEF DESCRIPTION OF THE DRAWINGS

Understanding of the present invention will be facilitated byconsideration of the following detailed description of a preferredembodiment of the present invention, taken in conjunction with theaccompanying drawings, in which like reference numerals refer to likeparts and in which:

FIG. 1 is a block diagram of function of the childbirth assisting systemof the present invention;

FIG. 2 is a plot of pressure versus contraction duration;

FIG. 3 is a block diagram of the components of the invention;

FIG. 4 is a block diagram of the pressure feedback loop of the prototypesystem;

FIG. 5 is a diagrammatic front view, partially cut away, of a firstembodiment of the girdle for use with the present invention;

FIG. 6 is a side elevation of a second embodiment of the girdle;

FIG. 7 is a diagrammatic front view of a third embodiment of the girdle;

FIG. 8 is a perspective of a fourth embodiment of the girdle;

FIG. 9 is diagrammatic side elevation of an alternate embodiment of thebladder/sensor combination; and

FIG. 10 is an exemplary plot of an indication of backpressure forassuring single use.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is a block diagram of the childbirth assisting device including apatient and a uterine contraction monitor 2. A closed loop system usespatient response and rule-based decision making methods to achieveoperator specified responses. The inventive device is a pneumatic closedloop system which is composed of an abdominal girdle 3 and acontroller 1. The controller 1 possesses five main functions:

1. Receiving the uterine activity data from the uterine contractionmonitor 2 and detecting the onset and offset of contractions.

2. Synchronizing the girdle pressure with the contraction, increasingthe girdle pressure at the onset of contraction and decreasing it at theoffset of contraction.

3. Adjusting the girdle pressure automatically to obtain theintrauterine pressure at a preset level.

4. Displaying information, including the girdle pressure.

5. Setting an alarm or alert system for abnormal situations.

The uterine contraction activity can be monitored either internally orexternally. Internal pressure monitoring provides the most accurateassessment of uterine activity by allowing pressure changes in theuterus to be transmitted via a fluid-filled catheter to a strain gaugetransducer. This produces quantitative readings of the duration,frequency, and amplitude of the uterine contraction, as well as thebaseline tone of the uterus. An external tocodynamometry, which can beapplied easily at any stage of labor, provides a non-invasive method ofassessing uterine contractions. This yields a fairly reliable estimateof frequency of the contractions but a less accurate reading of thecontraction intensity than an intrauterine catheter. The actualamplitude of the contraction cannot be measured by this method. In thepreferred embodiment, the controller 1 receives the uterine activitydata from an internal pressure monitor 2. The internal pressure monitorprovides the accurate intrauterine activity data to the controller,which are necessary for improving the safety and efficiency of inventivedevice.

Alternately, the inventive system may operate on an open loop principlewhich comprises a modification of functions 2 and 3 listed above. In theopen loop system, application and release of girdle pressure need notrely on intrauterine pressure. Instead, application of pressure to thegirdle will be triggered by detection of contraction pressure by theexternal toco sensor only, and only after a pre-determined thresholdpressure is attained and held for a specified period of time. Onceinflated, the girdle pressure is maintained for a fixed duration, e.g.,30 seconds, after which the release valve is automatically opened todeflate the girdle. The prototype embodiment of FIG. 4 is an open loopsystem.

The normal uterine contraction curve is bell-shaped, as shown in FIG. 2,with the descending limb returning to the same basal level as precededthe ascending limb. At the beginning of the first stage of labor withcervical dilation up to 3 cm, an average increase in maximum uterinepressure above basal level is about 20-30 mmHg while at the activephase, with cervical dilation from 3 cm to 10 cm and the second stage oflabor, it is in the range of 40-50 mmHg. Contraction frequency alsoincreases from two to three per 10 minutes to four to five per 10minutes at the end of labor. On slow rise of uterine pressure, thecontroller evaluates the uterine activity data and determines the onsetof contraction. Once the controller 1 detects the onset of contraction,the girdle pressure will be increased. Determining the onset ofcontraction is somewhat arbitrary. This invention may not be recommendedfor use during the early first stage of labor including the early activephase (cervical dilation up to 6-7 cm). In the preferred embodiment, theonset of contraction is set at 15-20 mmHg above the basal level. At theonset of contraction, the girdle pressure is increased at the presetrate until the preset intrauterine pressure is obtained. Once theintrauterine pressure reaches the preset pressure, the girdle pressurewill be maintained to obtain a constant intrauterine pressure. Theoffset of contraction can be detected when the girdle pressure increasessharply, as shown in FIG. 2. The girdle pressure will be released upondetection of the offset of contraction.

The girdle 3, illustrated in detail in FIG. 5, is formed of two basiccomponents: the belt 100 and the bladder 102. The design of the beltrequires two considerations. The inner lining must be soft andcomfortable to the mother while the outer lining must have high tensilestrength so that it can be tightly secured around the mother to keep thebladder inflation pressure downward against the abdomen. The belt 100may be formed from polyvinylchloride (PVC) or an elastomer-coatedfabric, such as polyurethane-coated nylon. For the patient's comfort,the interior lining of the belt which comes in contact with the skinshould be a soft fabric, such as the loop material of a hook-and-loopfastener, velour, woven fabric such as cotton or nylon, netting, or acombination of materials including a laminate. The choice of materialswill depend on the integration of the bladder. For example, the beltcould serve as the reinforced lining to the bladder, or it could be partof the bladder. An elastomer coating on outer layer of the belt may beadded to prevent the fabric from stretching, or the outer surface may benon-stretch cotton fabric or surgical tape. In one version illustratedin FIG. 5, the belt is originally formed in two layers 101 and 103 sothat the bladder 102 may be inserted between the layers. (Layer 101represents the outer PVC layer and layer 103 represents the innerfabric-lined layer.) The layers may be sealed together after the bladderis inserted to firmly retain the bladder at a fixed position within thebelt. The sealing welds 105 are indicated as dashed lines.Alternatively, the bladder 102 may be floating, sealed to only one ofthe two layers of the belt, or unattached to either layer and simplyretained between the two layers once they have been sealed together.Selection of belt configuration may be made based upon pressure transferefficiency, with the floating bladder version having demonstratedimproved pressure transfer in prototypes of the invention. The choice ofmaterial of which the belt is made will depend upon whether the bladderis attached or floating.

In another embodiment shown in FIG. 6, the inner and outer layers 101'and 103' are sealed together without placing the bladder between thelayers. The bladder 102 is held directly against the mother's abdomen,with the inward force of the belt providing means for maintaining thebladder in the proper location.

Belt tension is critical to the performance of the belt. In order tofacilitate the best possible fit to the mother, the end of the belt maybe split to form two separately adjustable straps 104 and 106, as shownin FIG. 5. Strips of Velcro®, or a similar hook-and-pile fastener 110,are sewn onto end 108 of the belt and onto the ends of straps 104 and106. The split design allows for the closest possible fit. The fasteneron straps 104 and 106 should have sufficient length to adjust the beltdiameter as needed for a particular patient. In order to optimize thefit of the belt, finger loop 109 is formed in end 108 to provide ananchor for medical personnel to use while pulling the straps to thedesired tension. The loop 109 may be formed by doubling over a smallportion of the belt material, then welding it in place.

Due to the significant amount of monitoring equipment that is usedduring a delivery, it may become difficult to place certain sensors onthe patient's abdomen in conjunction with the belt 100. One method foralleviating this is by providing tabs 112 and 114 at the lower edge ofthe belt 100 which permit attachment of the toco sensor directly to thebelt, eliminating the need for an additional toco belt. The toco sensor116, which monitors the contractions, is mounted on an elastic fabric118 with eyelets 120, 121, adhesive strips, hook-and-pile fasteners orsnaps at either end which attach to corresponding fasteners 122, 123 ontabs 112, 114. With a standardized length between the eyelets 120, 121,since the tabs 112, 114 are at a fixed distance (17.5" in the preferredembodiment), this provides a further advantage in that the toco sensoris always maintained at the same tension against the mother's abdomen.

The expandable bladder 102 may be formed from a thin reinforcedpolyurethane, polyvinyl chloride (PVC), silicone, or similar elastomericmembrane material. In the embodiment of FIG. 5, the bladder issandwiched between and welded to the belt material so that the bladdercannot move within the belt. Inflation nipple 128 extends from bladder102 through an opening in the belt 100.

The material of which the preferred embodiments of the belt and bladderare made are selected to permit the girdle to be economicallymanufactured as a single-use, disposable item. For safety reasons, toassure that the girdle is not weakened or degraded by multiple uses, theinflation nipple 128 can include means for assuring that a girdle isused only once. The single use means can be a break seal/plugincorporated into the inflation nipple 128 which, once connected to themonitor and air supply hoses must be broken to remove it, preventing itsreuse. Other means for assuring single uses of the girdle can be a peelaway connector in the inflation nipple 128, a piezo film, or a rupturefilm built into the nipple 128. The rupture film 129 (showndiagrammatically as dashed lines in FIG. 5) spans the interior of thenipple 128 and works in cooperation with the controller 1. When the airsupply hoses 24A and 24B are connected to the girdle (referring to FIG.3), an initial burst of air can be provided to rupture the film 129. Thesense valve 9 will detect a backpressure and the controller 1 will havestored data regarding a pre-set pressure threshold value at whichrupture of the film should occur. If the threshold backpressure is notattained, this may be an indication that the film 129 was alreadyruptured in a previous use of the girdle. Software within the controller1 will prevent any further use of the system until a new girdle isdetected by way of the proper backpressure. An exemplary plot ofdetection of a seal by backpressure showing hypothetical upper and lowerlimits (UL and LL) for as thresholds for confirming correct backpressureand time to rupture is provided in FIG. 10.

A piezo film would function in a similar manner, with the film, itself,providing the signal indicative of the pressure being applied during theinitial burst. Alternately, an electrically conductive strip could bebuilt into the nipple 128 which can be detected by causing a change inresistance of electrical wiring built into the air tubing.

An alternate solution to the problem of a limited area on the mother'sabdomen on which a number of different devices need to be place is toutilize the bladder 102 itself as part of the contraction sensor. Thisis favorable because the bladder membrane is sound sensitive and willconduct the acoustic waves for pick-up by a sensor 130 built into thebladder, as shown in FIG. 6.

A second alternate solution to working within the limited space is toform the bladder with fan-folds 132 or accordion pleats, as illustratedin FIG. 7. Here, when the bladder is deflated it covers only a smallarea of the abdomen. Upon inflation, the bladder expands within the beltinto the area indicated by dashed lines 136 to apply pressure in theappropriate direction. A pocket within the belt controls the directionof expansion of the bladder to assure that the pressure is disperseduniformly and in the proper direction. When the bladder is inflated, thereadings from the toco sensor are not as critical, so expanding thebladder over the toco sensor is not a problem.

The girdle may also incorporate one or more separate bladders 140 whichare controlled independently of the primary labor-assisting bladder 102to regulate overall belt pressure and to add lumbar support. Thisembodiment is shown in FIG. 8. Note that the primary bladder 102 isshown in a slightly different configuration from the typical triangularshape. The shape of the primary bladder is not limited to a triangle,nor must the size be fixed. It can be varied as needed to apply thedesired pressure appropriately. Secondary bladders 140 help repositionthe patient during periods of discomfort. Inflation of bladders 140 canbe coordinated with contractions to alleviate lower back pain associatedwith the contractions, or inflation can simply occur at fixed intervalsto provide a massaging function. Bladders used for regulating belttension can alleviate pressure from the epidural and spinal column,making belt application easier.

The sensor for detecting contraction and fetal heartbeat may beincorporated into the girdle as described above in the form of a tocosensor, or may utilize ultrasound, pressure sensitive ink or piezo film150, which may be incorporated into the fabric of the belt or in thebladder 152 (see FIG. 9), or air/fluid displacement. The piezo film 150may be polyvinylidene fluoride (PVDF), which transducers are known inthe art. A representative discussion of such transducers for fetal heartsound detectors and uterine contraction monitors is provided in thearticle entitled "An Application of PVF₂ to Fetal PhonocardiographicTransducers", F. Steenkeste, et al., by F. Steenkeste and Moschetto.Three approaches for placement of the sensor(s) are: multiple smallpockets located below the main bladder, a Velcro®-backed sensor that canattach to a loop lining on or around the main bladder, or a sensorsealed inside the main bladder, such as shown in FIG. 6. Multiplesensors may be used in series for greater reliability. Air pockets andbladders are ideal for housing small sensor because they can accuratelyand consistently apply the force necessary for reliable signal response,and they provide the direct capability to synchronize operations withthe main bladder.

FIG. 3 is a block diagram of automatic labor assisting device, showingthe details of the controller 1 and the girdle 3 according to thepresent invention. Within controller 1, a pressure sensing means,including pressure transducer 11 and analog signal conditioner 12,produces a signal which is fed into the microprocessor 22. The signal isquantized in a 12 bit analog-to-digital converter within themicroprocessor 22. A display means, which includes a memory and signalprocessing circuitry within the microprocessor 22 and display 13,produces a pressure display of the girdle's internal pressure. A memory40 within the controller provides storage for control parameters and alibrary of diagnostic information, which is described below in moredetail. An inflatable girdle 3 is shown connected via tubing 24A and 24Bto the controller 1 at coupling 25A and 25B. Coupling 25B is connectedvia valve 9 and pressure line 26 to pressure transducer 11. A signalrepresenting the pressure measured by the pressure transducer 11 andanalog signal conditioner 12 is applied via electrical line 27 tomicroprocessor 22. Two of the control switches 15 are used to apply asignal to microprocessor 22 to set a target intrauterine pressure and amaximum girdle pressure. A signal representing intrauterine pressure isapplied to microprocessor 22 via connector 28 and electrical line 29.

Microprocessor 22 is programmed to calculate the girdle pressureadjustment proportional to the magnitude of the difference between theintrauterine pressure and the selected target pressure, and produces anoutput signal on line 30 which indicates the girdle pressure adjustment.A select switch in control switch 15 determines if an external air linevia air line 42, an internal replaceable air bottle via air line 21, oran internal motor 5 and pump 6 are to be used to inflate the girdle.Note that all three air paths are isolated from each other via checkvalves 18, 19 and 32. The motor 5 is turned on and off by themicroprocessor 22 via line 31 to a motor and valve driver circuit 4. Thepressure to the girdle 3 is controlled by the regulator 17. Valve 7vents the pressure in girdle 3 via vent 8 for a time determined bymicroprocessor 22 through line 52.

Power is applied to controller 1 through line 33 via switch 34 andcircuit breaker 35. A voltage regulator 36 provides a 5 volt regulatedvoltage which is used to power the portion of the digital circuitrequiring a positive 5 volts. The 12-volt voltage output is alsoprovided for portions of the circuitry such as the valves, pumps andpressure transducer which require 12-volt power supply. Differentialpressure switches 44 are connected between lines 37A and 38B. If anyobstruction occurs between lines 37A and 37B, switches 44 apply a signalto microprocessor 22 through line 38 to sound an alarm.

The microprocessor 22 utilizes the information and the signals appliedto it to control the girdle 3 and to provide information output. Signalsapplied from microprocessor 22 to the displays 13 and printer 16include:

Target intrauterine pressure

Maximum girdle pressure

Current intrauterine pressure

Uterine pressure due to primary force

Current girdle pressure

Diagnostic information for doctor

Alarm for whether there is an obstruction (kink).

The microprocessor 22 compares the input signal received from theintrauterine monitor and the girdle pressure sensors against criteriawhich are stored in the memory 40. These criteria include the variouspressure settings, as well as means for identifying the presence ofabnormal contractions which may require modification of the operatingparameters of the controller or may require removal of the girdle.

Signals are generated to sound alarm 14 whenever alarm conditions aremet. The alarm may be silenced if desired via one of the controlswitches or by pressing an emergency stop button which will deactivatethe controller and deflate the girdle. Sense valve 9 is connectedbetween girdle 3 and pressure transducer 11. The sense valve 9 connectsthe pressure transducer 11 to atmosphere through vent 10 during thegirdle start-up sequence in order to correct the pressure transducerzero offset. Overpressure valve 39 is connected to the line 50 betweenregulator 17 and inflate-deflate valve 7. This is a manually adjustablevalve which limits the maximum pressure delivered to the girdle, in theevent that all the safeguards in the air regulation line systems fail.In addition, safety valve 23 is designed into the girdle 3 to deflatethe girdle in case of extreme overpressure which would endanger thefetus.

A prototype of the controller was designed with two feedback controlloops. The first loop monitored and evaluated the activity of theuterine contraction. Intrauterine pressure was detected by a straingauge operated with a bending beam mechanism. The output signal of thestrain gauge ranged from 1 V at zero pressure to 5 V at 105 g of force.The signal generated by the strain gauge was digitized and transferredto the built-in microprocessor. The programming within themicroprocessor caused the second feedback loop to be initiated once theintensity of the contraction reached a certain point (20% of full scale)and stayed over that point for 5 seconds. Using this criteria, a falsesignal generated by non-contraction processes such as physical movementby the patient could be filtered out.

The second feedback control loop, shown in FIG. 4, controlled theinflation and deflation of the girdle 3 using an air compressor 60. Thisloop is a slight modification of the system of FIG. 3. The girdle isconnected to the air compressor 60 (Gast Manufacturing Corp. diaphragmcompressor, 50 PSI maximum with 15 cubic inches per second air flow)through air line 80 with air valve 67 controlling the rate of inflationof the girdle 3. The girdle 3 may be deflated through air line 82 byopening air valve 77 and venting the girdle to atmospheric pressure.Each line is connected with its own transducer 72 or 76, each with anoutput of 1 V per 100 mmHg (Sensym, output range of 1 to 15 volts with abase voltage of 1 volt at 0 mmHg). Transducer 76, attached to air line82, reads the air pressure coming into the girdle from the aircompressor. When the onset of contraction is detected and meets the truecontraction criteria, air passes through air line 80 until the internalgirdle pressure reaches the target belt pressure established by theoperator. When the girdle pressure reaches its target, air valve 72switches off to block the air flow into the girdle.

If the girdle pressure drops, transducer 76 detects the drop, and airvalve 67 is activated to re-pressurize the girdle to target pressure. Asa safety mechanism, valve 77 opens 30 seconds after initiation of theinflation process to deflate the girdle.

To detect the occurrence of tube kinking, the microprocessor sets aminimum pressure increase of 10 mmHg for 5 seconds. Any rates below thisare treated as tube kinking, triggering immediate deflation of thegirdle and activating an audible alarm for 5 seconds or longer. If thissafety device fails, an emergency stop button is provided. The emergencystop button opens valve 77 and closes valve 67 for emergency deflation.

Displaying various forms of outputs is an important function of thecontroller 1. The girdle pressure and the patient information aredisplayed on the screen.

To detect hazardous conditions or unexpected patient responses, numerousalert and alarm criteria may be optionally implemented within the devicecontrol software:

1. Setting a maximum duration at the target intrauterine pressure duringthe contraction: A normal contraction may last about 60-90 seconds.However, abnormal contractions such as polysystole, skewed contractionsand tachysystole may show a longer contraction period due to a slowreturn to a baseline. This may result in applying the high pressure ontothe abdomen over an extended period. To avoid this problem, the maximumduration at the target intrauterine pressure during the contraction willbe established at 20-60 seconds. In the prototype, the limit was set at30 seconds.

2. Setting an interval between two cycles of girdle pressure increase:Contraction frequency increases from two to three per 10 minutes to fourto five per 10 minutes at the end of labor. Abnormal contractions suchas paired contractions show much a shorter interval between twocontractions. The use of the labor assisting device in this case mayresult in applying an excessive force to the abdomen in a short timeperiod. This problem will be solved by setting a minimum intervalbetween two cycles of girdle pressure increase. The minimum intervalwill be set at 1.5-5 minutes, with the prototype set at 1.5 minutes.

3. Setting the target intrauterine pressures at different stages oflabor: In normal labor, an average increase in maximum uterine pressureabove basal level begins with about 20-30 mmHg at the early first stageof labor and becomes 40-50 mmHg at the active phase and the second stageof labor. This force is mainly produced by the primary and involuntaryforce. In addition to the primary force, the use of the inventive devicewill increase the intrauterine pressure further by providing thesecondary force. To enhance the safety of the device, the targetintrauterine pressures are assessed during various phases of labor. Forexample, the target intrauterine pressure during the stage of labor withcervical dilation from 3 cm to 8 cm is set at 40-60 mmHg above thebaseline while during the active phase with cervical dilation from 8 cmto 10 cm at 60-80 mmHg and the second stage of labor at 80-160 mmHg. Thedecision of whether the stage of labor is early or active should be madeby a physician. Obstetricians also set up the appropriate targetintrauterine pressure depending on clinical situations. Anyuncontrollable intrauterine pressure increase above the target pressure(15 mmHg higher than the target) will trigger the alarm system andrapidly deflate the girdle.

4. Setting a limit of the girdle pressure at each target intrauterinepressure: This mechanism also prevents any extra force on the abdomenwhich may result from malfunctions of the device. For example, the limitof the girdle pressure will be set at 150 mmHg during the stage of laborwith cervical dilation from 3 cm to 8 cm when the target intrauterinepressure is 40-60 mmHg. The limit will be set at 250 mmHg during theactive phase of labor with cervical dilation from 8 cm to 10 cm when thetarget intrauterine pressure is 60-80 mmHg. The limit will be set at 350mmHg during the second stage of labor. The girdle pressure above theselimits triggers the alarm system and rapidly deflates the girdle. Thegirdle may also be implemented with its own safety valve which be blownif the pressure exceeds 350 mmHg. In the prototype, the safety valve wasimplemented by setting the maximum pressure of 350 mmHg in thecontroller software and by an inline air regulator 66 (in FIG. 4). Ifthe girdle pressure exceeded 350 mmHg, valve 77 opened to deflate thegirdle.

5. Filtering the false contractions: The movement of patient sometimesgenerates the sudden rise of intrauterine pressure. This can be filteredby evaluating the rate of intrauterine pressure increase, defined as aderivative, dP/dt, where P=intrauterine pressure and t=time, andcomparing with a normal range of the rate. Any contractions with therate of intrauterine pressure higher than the normal range will betreated as false contractions and will not trigger the inflation of thegirdle.

In the prototype, a fault signal generated by non-contraction processesis filtered by setting a 5 second delay rule, i.e., a true contractionoccurs if the intensity of the signal remains at 20% of full scale for 5second.

For the safe use of the childbirth assisting device, several abnormalclinical situations have been considered. The criteria for each of thesesituations is stored within a library in the controller's memory 40 andthe contraction data is compared against these criteria to determinewhether the abnormal condition is present. If so, an alarm condition isinitiated and an output is provided to indicate the presence of theabnormal condition. The following situations are included in the libraryof abnormal conditions:

1. Hypotonia/Hypocontractility:

When contractions are less than 25 to 30 mmHg at their peak, or recurless frequently than every five minutes in the active phase of labor andlast less than 45 seconds, hypocontractility is present, even if it isaccompanied by progress in labor. The decreased uterine activity may bedue to the abnormal contraction, hypotonia, or the artifact from thepresence of air in the internal monitoring system. In both cases, theuse of the device may not cause safety problems. However, since thedevice will not allow the girdle pressure to exceed the safety limit,the alarm system will be on before the target intrauterine pressure isobtained. The correction should be made upon a proper diagnosis of theabove problems. The presence of air in the internal monitoring systemcan be corrected easily and device can be restarted.

2. Polysystole:

Polysystole is a common abnormal uterine waveform that is characterizedby a single contraction with two or more peaks. It is also described astwo or more contractions in juxtaposition without full return to thebaseline between each. This could be determined by software and if thesituation meets the alarm criteria set in the above section, the girdleshould deflate and a physician should be informed.

3. Discoordinate uterine activity:

The constancy of the intervals between uterine contractions determinesthe degree of coordination or rhythm of uterine activity. When a markedvariation occurs from contraction to contraction, the resultant patternis termed "discoordinate labor". Because contractions may be generatedfrom alternate uterine cornua as well as from other sites, frequent lowintensity contractions are a typical finding. Since the controller setsup a threshold to evaluate the onset of contraction, some of thelow-intensity contractions below this threshold may not trigger thegirdle pressure to increase. This will be similar situation ofhypotonia. In this case, the use of the device may not cause any safetyproblem. Other discoordinate labor, Uterine hypertonus, may result fromthe constantly contracting state of some area in the myometrium. Extremedegree of this phenomenon is uterine fibrillation. In this case, the useof the device should be avoided.

4. Skewed contractions:

A skewed contraction is characterized by a prolongation of thedescending limb (relaxation phase) of the uterine contraction and isoften seen in a mixed pattern with polysystole. The use of the inventivedevice implemented with a maximum duration at the target intrauterinepressure will not cause any problem.

5. Paired contractions:

Paired contractions are a form of increased uterine contractionfrequently characterized by one uterine contraction in close temporalrelationship to a second uterine contraction, with the waveformreturning to baseline between the two contractions. Usually, the secondcontraction is smaller in amplitude. Since the device sets the minimuminterval between two cycles of girdle pressure increase, its use underthis condition will not cause any safety problem.

6. Tachysystole:

Tachysystole is defined as increased uterine contraction frequency.Because of the inevitable accompanying diminished or absent restinginterval, decreased fetal oxygenation has been associated more oftenwith this form of uterine hyperactivity than with increased intensity orduration of the uterine contraction. However, increased uterine activityof any type does not infer fetal stress or distress. Increased uterineactivity may well be tolerated by some fetuses, whereas others maydemonstrate stress even with uterine activity of a low intensity. Aslong as the fetus does not show distress, the use of the inventivedevice will not cause any problem. The software in device will diagnosethe situation. However, a physician should make a final decision.

7. Tachysystole with progressive hypertonia:

Progressive hypertonia, usually associated with tachysystole, is a formof uterine dysfunction. It represents incomplete relaxation betweenfrequently occurring contractions. The software in the inventive devicewill diagnose the situation. However, a physician should make a finaldecision about continued use of the device.

8. Tachysystole with progression to tetany:

Progressive uterine hypertonus, characterized as a rising baseline tone,is often accompanied by tachysystole. During the relaxation phase, theuterine tone does not completely return to the prior resting phase levelbefore the next contraction begins. This may progress to tetany. Thesoftware in the inventive device will diagnose the situation. The use ofthe device should be decided by a physician under this circumstance.

9. Peaked contractions:

A contraction pattern of high intensity and frequency, with a peakedcontour, has been associated with preeclampsia and eclampsia. Thesoftware in the labor assisting device will diagnose the situation. Theuse of the device should be decided by a physician under thiscircumstance.

10. Hypersystole:

The amplitude of intensity is the pressure difference (in mmHg) betweenthe peak of the uterine contraction and the uterine tone preceding thecontraction. Hypersystole is defined as greater than 60 mmHg maximumpressure. Contractions of greater than 60 mmHg are seen withpharmacologically overstimulated or spontaneous abnormal labor. If thereis enough uterine pressure, the use of the device is not necessary. Aphysician will make a decision on continuing the use of the device.

The childbirth assisting device of the present invention effectivelyprevents prolonged duration of labor and dystocia due to systemicanalgesia, epidural anesthesia, or maternal exhaustion, leading toreduction of the cesarean section rate and rate of instrumentaldelivery. Since weakening of the secondary labor force is particularlycommon in patients receiving epidural anesthesia, the device caneffectively prevent weakening of the secondary labor force underanesthesia, enabling a safer and less painful delivery. The inventivedevice includes means for analyzing the contraction curve and period inorder to identify the presence of abnormal conditions, providing furthersafety benefits.

By reinforcing the secondary labor force, the childbirth assistingdevice can further reduce the rate of cesarean section associated withdystocia and also lower the dosage of oxytocin. Functioning throughdifferent mechanisms, the device can be used to complement the benefitsof oxytocin in clinical practice,

It will be evident that there are additional embodiments andapplications which are not disclosed in the detailed description butwhich clearly fall within the scope and spirit of the present invention.The

specification is, therefore, not intended to be limiting, and the scopeof the invention is to be limited only by the following claims.

We claim:
 1. An improved girdle for use in a system for assisting inchildbirth, the system comprising a girdle having at least oneinflatable bladder adapted to be positioned over a patient's abdomen forapplying pressure to the abdomen, a contraction monitor for generatingan electrical signal indicative of the patient's contractions, anautomatic controller means in electrical communication with saidcontraction monitor for controlling the inflation and deflation of saidat least one inflatable bladder in response to said electrical signalwherein the pressure is increased to a target intrauterine pressure atthe onset of a contraction and decreased after the contraction is over,said automatic controller means having means for controlling air from anair source for inflating said girdle, and tubing having a first endattached to said girdle and a second end attached to said automaticcontroller means for conducting air between said girdle and saidautomatic controller means, the improved girdle comprising:a belt havinga first end, a second end, an upper edge, a lower edge, an inner layerand an outer layer, said inner layer having a soft contact surface forplacement against the patient's abdomen, said outer layer being anon-expandable material, wherein said inner and outer layers are sealedtogether at at least said first and second ends and said upper and loweredges; fastening means disposed at each of said first and second endsfor releasably fastening said first end to said second end so that saidbelt fits closely around the patient's abdomen; and an inflatablebladder held by said belt at a position of said belt corresponding tothe patient's abdomen so that said inflatable bladder is immovable, saidinflatable bladder having an inlet means for connecting to said firstend of said tubing for admitting air into said bladder.
 2. An improvedgirdle as in claim 1 wherein said second end of said belt is split toform two separately adjustable belt sections.
 3. An improved girdle asin claim 1 further comprising a finger loop formed in said first end ofsaid belt.
 4. An improved girdle as in claim 1 wherein inner layercomprises a fabric.
 5. An improved girdle as in claim 1 wherein saidbladder is sandwiched between said inner and outer layers of said belt.6. An improved girdle as in claim 5 wherein said bladder is attached toat least one of said inner and outer layers.
 7. An improved girdle as inclaim 1 wherein said bladder is retained between said inner layer andthe patient's abdomen.
 8. An improved girdle as in claim 1 wherein saidinlet means has a rupture membrane for providing a backpressure to apre-determined level upon introduction of air.
 9. An improved girdle asin claim 1 further comprising a pair of tabs extending from said loweredge of said belt and having second fastening means for attachment ofthe contraction monitor when the contraction monitor is a toco sensormounted on an elastic band.
 10. An improved girdle as in claim 1 furthercomprising at least one second inflatable bladder disposed within saidbelt at a position of said belt corresponding to a lumbar region of thepatient.
 11. An improved girdle as in claim 10 further comprising asecond controller means for independently controlling inflation of saidat least one second inflatable bladder and a second tubinginterconnecting said at least one second inflatable bladder and saidsecond controller means.
 12. An improved girdle as in claim 1 whereinthe contraction monitor is disposed within said bladder.
 13. An improvedgirdle as in claim 12 wherein the contraction monitor is a piezo film.14. An improved girdle as in claim 1 wherein said inflatable bladder hasa plurality of pleats therein.
 15. An improved girdle as in claim 1wherein said inner and outer layers of said belt are welded together.16. A girdle for use in conjunction with a controller for regulating airpressure in response to detection of an electrical signal indicative ofa contraction during childbirth, the girdle comprising:a belt having afirst end, a second end, an upper edge, a lower edge, an inner layer andan outer layer, said inner layer having a soft contact surface forplacement against a patient's abdomen, said outer layer being anon-expandable material, wherein said inner and outer layers are sealedtogether at at least said first and second ends and said upper and loweredges; fastening means disposed at each of said first and second endsfor releasably fastening said first end to said second end so that saidbelt fits closely around the patient's abdomen; an inflatable bladderheld by said belt at a position of said belt corresponding to thepatient's abdomen so that said inflatable bladder is immovable, saidinflatable bladder having an inlet means for connecting to said firstend of a tubing connected to said controller for admitting air into saidbladder; and a contraction monitor attached to said bladder andelectrically connected to the controller for detecting uterinecontractions and generating the electrical signal to which thecontroller responds.
 17. A girdle as in claim 16 wherein saidcontraction monitor is a piezo film.
 18. A girdle as in claim 16 furthercomprising means disposed within said inlet means for preventing reuseof the girdle.